The long term objective of this research is to develop a reliable DNA probe test for the prediction of the debrisoquine metabolism phenotype. The specific aims of the research are to (1) develop methods for probing the CYP2D6 locus encoding debrisoquine hydroxylase independently of the highly homologous but apparently unexpressed CYP2D7 and CYP2D8P loci; (2) develop a mammalian cell expression system for genomic copies of the CYP2D6 locus to evaluate the effect of mutations; (3) determine if the missing "C" residue in intron 5 of CYP2D6 variant "a" results in retention of intron 5 in mRNA, and if so, develop a DNA probe test to detect the variant "a" sequence; (4) clone and sequence the other mutant alleles of CYP2D6 to determine the mutations responsible for loss of enzyme activity; and (5) develop a multiplex DNA probe test permitting detection of all mutant alleles in a single hybridization. The first three aims should be completed in Phase I of this research program. In Phase II, the causative mutations for the other mutant alleles will be determined, and DNA probe tests will be developed by using the tools developed in Phase I. A DNA test for debrisoquine metabolism will permit prediction of an individual's metabolism rate for more than 20 commonly used drugs. The test will be applied to a small volume of whole blood and, unlike the current metabolism test, will not suffer from interference by other drugs taken by the patient. A DNA probe test for such a common genetic defect with many mutant alleles will be an excellent model system for development of new multiplexing methods.